The present invention relates to the technology of providing high-availability (HA) clusters, and more particularly, to a method, apparatus and computer program product for providing high availability in an active/active appliance cluster.
An active/active appliance cluster is a cluster of appliances (e.g., servers) in which a primary appliance and a secondary (e.g., failover/backup) appliance are both actively running a same operation/application/service.
In a large data center, high-availability clusters usually ensure that multiple servers or appliances can meet business needs. A high-availability cluster is equipped with sufficient components, implemented, and deployed to thereby meet a functional requirement: sufficient redundancy of components (hardware/software or procedure) to mask defined faults. The purpose of the high-availability cluster is to minimize server-related or appliance-related downtime caused by system errors and reduce business loss caused by the system errors. At present, some commercially available products provide the aforesaid function and characteristic.
In general, an appliance, or known as Internet appliance, features built-in networking capability, and has a specific function; and its examples include gateway, router, network attached storage, access point, digital TV set top box, and network file sharing server. For more details about appliances, please make reference to IBM® WebSphere® DataPower Series SOA Appliances or Tivoli® ISS Appliances® (IBM, WebSphere, and Tivoli are registered trademarks owned by International Business Machine in the United States and/or other countries.)
Unlike general-purpose computer devices, an appliance is typically designed to serve a specific purpose or provide a specific service and thus is more robust. Compared with general-purpose computer devices, “appliances” are relatively “closed”—their specific operating systems and applications (or drivers) vary with their intended purposes and services.
In a cluster with multiple appliances, high availability represents an important dimension in deployment of appliances. This is especially true to those appliance products which serve as the processing units of an enterprise in a demilitarized zone (DMZ). As regards a conventional cluster with multiple appliances, a high-availability cluster is usually built with a centralized external persistent storage (such as a self-contained database). From the perspective of an active/active appliance cluster, assuming that transactions processed by an appliance are stateless, as are in the case of typical http webpages, an external load balancer is in use before the cluster is formed with appliances, and thus the transactions can be easily redirected to the other appliances in the cluster.
Those appliances whose transaction persistent state has to remain unchanged are also required to create a high-availability cluster by means of an external system (such as a database). To this end, it is necessary for appliances in the high-availability cluster to exchange states efficiently, for failover implementation to be transparent to an external partner, and for a system architecture to be scalable in order to support deployment of n nodes without imposing great impacts on performance.
Not only does system maintenance pose a problem, but synchronization of data between active/active appliance clusters is also inefficient; hence, users anticipate a solution whereby active/active appliances are self-contained and thus do not rely upon any external system, such as a centralized external persistent storage (say, a self-contained database), and a load balancer. Furthermore, the users also expect that the solution is scalable to n nodes for deployment.